There is the "load heavy for caliber" for penetration concept. These days I'm seeing some pretty heavy weights for handgun bullets. 700gr 500 S&W and 200gr 357 magnum. Is there some point where the bullet can be too heavy, even when moving at a velocity where it is viable as a game bullet? I hope I asked my question so it's understandable.

An example of a projectile that's heavy for caliber is a crossbow bolt. Even more extreme is an arrow.

I think the first limit one would reach in a firearm would be ability to put a round in the magazine or cylinder. The round can't exceed their lengths. For a single-shot, the leade, or length between the case mouth and start of the rifling, must be long enough to fit a long bullet.

A very long bullet would have too much friction if it were groove diameter all its length, but if it has reasonable driving bands at groove diameter, and the rest of the bullet were bore diameter, it could be shot without excessive friction. Many cast rifle bullets are designed that way, as are artillery shells.

Another limiting factor is stabilizing the bullet. Most firearms stabilize by spinning the bullet with rifling. But, conventional bullets can't be spun fast enough after reaching a certain length. Crossbow bolts, arrows, and shotgun slugs are stabilized by feathers or by putting their weight well forward in the projectile. Modern tanks' guns use fins on their bullets, and use sabots to hold the bullet in the bore and to seal around the fins. These are all aerodynamically stabilized, not spin stabilized.

So, as long as lengths and friction are addressed, one can make the bullet as long as one wants. For example, whale harpoons don't even fit in their launchers' barrels.

You asked a very interesting question.

Yes, the trend these days, especially on a board like this that offers cast bullets for reloading, is for heavier and heavier bullets.

As far as diminishing returns on these, the obvious answer is lower velocities. You can only get so much powder and bullet in a case, especially handgun cases. Another factor is rate of twist to stabilize the bullets due to longer and longer bearing surfaces.

With proper propellent adjustment, would suppose you could load up just about any feasible bullet weight and achieve some sort of accuracy. May have a trajectory like that of a ball bearing falling off the edge of a table, though! :D

Is there some point where the bullet can be too heavy, even when moving at a velocity where it is viable as a game bullet? .

I think a bullet can be too heavy for the caliber. Certainly the jacketed bullets can be too tough.

Your .357 magnum example is a good one. When whe shot iron targets I shot the .357 Maximum and .357 Herrett with all weight bullets. While the 200 grain Hornady bullets gave us good accuracy I always felt I had better on-target performance with 180 bullets.

In the .356 and .358 Winchester I feel 230 grains is as heavy as I need. I found that our smaller white tail deer dropped quicker with lighter bullets. The 225 Sierra in the .358 loaded with the 200 grain bullets in the .356 giving us quick kills on deer.
My Dad and brother used the .350 Rem Mag and .35 Whelen on Caribou in Alaska and both found the 200 grain bullets to kill Caribou quickly out to 200 yards or so.

In the .307 Winchester I dont need or want anything over 180 grains. I have read a lot about heavy bullets in the .30-30 but I am very happy with 170 grains as my upper weight limit. If I were going for heavier game like Grizz does I would use bullets of strong construction but stay with the 170 grain upper limit.

In the .444 Marlin I like the 310 grain Lee bullet very well.

For the .45-70 I get quicker kills on deer with the 322 grain Lyman Gould HP or the 350 grain NEI solid version of the same bullet.

In small cartridges such as the .32 H&R Magnum I want heavy for the caliber bullets. I prefer the 115 grain bullets in the .32 Magnum for tough critters such as racoon or porcupine.

Yes, you can be too heavy for caliber, but because the heavier bullets are usually longer, and may not stabilize with the rifling twist installed in your particular firearm. In addition, because the heavier bullets take up more space in the case, your powder charges will be smaller, both because of volume and pressure. This will in turn tend to decrease velocities, thus making heavier (longer) bullets which might have stabilized at a higher velocity in your twist unable to do so because of the reduction in velocity. Some examples are the older .444 Marlin rifles in which the twist given from the factory would stabilize up to 265 gr, but was marginal to poor for anything over that. I believe that Marlin increased the twist rate so that 300+ gr bullets would stabilize. Another is the older 1/14" twist in the M-16. It would stabilize up to 55 gr at the velocity of the M193 ball ammo, approx 3300 f/s, but when the newer tracer round that had a longer, somewhat heavier 63 gr bullet was introduced, it would not stabilize, and the government went to a faster twist rate, 1/7" to compensate for this. In doing so they lost some lethality as the bullets were overstabilized, and lost the wounding capability that the older 55 gr with 1/14" provided with ball ammo, as these were on the edge of stabilization, and tumbled badly after striking a solid target.

Besides stability...which is pretty well covered in the last post...does seem that there is a trade off for velocity with bullet weight.

Run the energy figures and you'll find a spot where energy starts to take a deep dive. Can get a 350gr. .444 bullet to spin true (if it's a blunt nosed bullet) and shoot accurately, but it's computed energy is much lower than with 290gr. or 300gr. (at allowable pressure). I think of it as the "break-over point".

Why? Run out of powder space. Have specific OAL that you have to abide by..so the heavier the bullet, the more case space it takes up and the less space for powder.

Not to say that those heavy-heavy weight bullets can't be useful...once you start a bullet of that weight and length, it's darned hard to stop it, so they do tend to penetrate pretty deeply. But they generally don't penetrate any better than bullets of slighly lighter weight (closer to the "break-over point").

Now a whole bunch of game was killed with bullets moving at about sonic speeds (call it 1100fps) during the black powder era...trajectory is the problem. Big slow heavy bullets drop, and you've better be right on the money in your range estimation if yout wnat to lob one of them into the kill zone.